A recent explosion of activity in the development of computational models of human perceptual, decision making, and response processes has been made possible by modern developments in cognitive theory and computer technology. A wide variety of programmed algorithms has been developed that simulate and describe what are usually only the parts and pieces of perceptually guided behavior. In the visual domain, for example, algorithms have been developed that perform such visual functions as edge enhancement (e.g., Argyle, 1971), object segmentation based on brightness, color, or texture (e.g., Landy & Bergen, 1991), and the generation of object depth from disparity, shading, or contour lines (e.g., Horn & Brooks, 1989). Other models have been developed that describe and analyze performance during motor tasks such as walking or manipulation or that imitate such performance in the form of a mechanical device.